git.sur5r.net Git - cc65/blob - libsrc/c1p/crt0.s

   1 ; ---------------------------------------------------------------------------
   2 ; crt0.s
   3 ; ---------------------------------------------------------------------------
   4 ;
   5 ; Startup code for Ohio Scientific Challenger 1P
   6
   7 .export   _init, _exit
   8 .import   _main
   9
  10 .export   __STARTUP__ : absolute = 1        ; Mark as startup
  11 .import   __RAM_START__, __RAM_SIZE__       ; Linker generated
  12
  13 .import    copydata, zerobss, initlib, donelib
  14
  15 .include  "zeropage.inc"
  16
  17 ; ---------------------------------------------------------------------------
  18 ; Place the startup code in a special segment
  19
  20 .segment  "STARTUP"
  21
  22 ; ---------------------------------------------------------------------------
  23 ; A little light 6502 housekeeping
  24
  25 _init:    LDX     #$FF                 ; Initialize stack pointer to $01FF
  26           TXS
  27           CLD                          ; Clear decimal mode
  28
  29 ; ---------------------------------------------------------------------------
  30 ; Set cc65 argument stack pointer
  31
  32           LDA     #<(__RAM_START__ + __RAM_SIZE__)
  33           STA     sp
  34           LDA     #>(__RAM_START__ + __RAM_SIZE__)
  35           STA     sp+1
  36
  37 ; ---------------------------------------------------------------------------
  38 ; Initialize memory storage
  39 ; copydata seems to be only necessary for special systems
  40
  41           JSR     zerobss              ; Clear BSS segment
  42           ; JSR     copydata           ; Initialize DATA segment
  43           JSR     initlib              ; Run constructors
  44
  45 ; ---------------------------------------------------------------------------
  46 ; Call main()
  47
  48           JSR     _main
  49
  50 ; ---------------------------------------------------------------------------
  51 ; Back from main (this is also the _exit entry):  force a software break
  52
  53 _exit:    JSR     donelib              ; Run destructors
  54           BRK
  55